Use the group trick.
First... (in your case)
Make sure RESISTANCE is hostile against WEST.
- place a WEST officer and group him with your police unit(s)
- Put in the init of that WEST officer :
deletevehicle this
or slide probabilty of presence to the left (0%), that's completely the same.
That's all.
EAST and RESISTANCE will fire upon you, because they think you are WEST.